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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bill Morris
Date: 2023 Oct 19, 12:32 -0700
"New sextant mirrors for old" on my sextant blog (www.sextantbook.com) details how to re-silver mirrors using tin foil and mercury. However, for rectangular mirrors at least, it is much simpler to cut new mirrors from 4 mm modern float glass mirror stock. Float glass seems to be flat enough for the purpose, as exposed in the post "How flat are sextant mirrors?" I suspect that much mirror glass from scientific suppliers is just common float glass such as can be had at very little cost by speaking nicely to your local glazier.
When cutting new rectangular mirrors it is as well to cut slightly oversize. Only a little elbow grease is needed to grind the edges square and to size, then bevelling the corners. The ground edges help backing paint to stick.
Circular mirrors are harder. They can be cut by hand, using techniques of amateur telescope makers, but it is much easier to use a home-made trephine rotated in a drill press or vertical milling machine.
Bill Morris
Pukenui
New Zealand
